Conveyor mechanisms for loading and unloading cargo are well known. Such conveyor mechanisms are commonly used, for example, to load and unload various products (e.g., bulk agricultural crops, aggregate material, construction material, boxes, crates, etc.) from a vehicle (e.g., a trailer, a semi-trailer, a wagon, a truck, etc.).
Such conveyor mechanisms typically include a pair of chain loops disposed within and along the floor (or bed) of the trailer. The chain loops are usually engaged by a pair of drive sprockets arranged on a first axle and also by a pair of associated idler sprockets arranged on a second axle. Because the axles are ordinarily disposed at opposite ends of the trailer, the chain loops are generally obround in shape. A plurality of transverse slats extending between links of the opposed chains provide support to the chain loops and enable the conveyor mechanism to transport heavier loads. Such conveyor mechanisms are commonly known as slat-type conveyors. Examples of these types of devices are provided by U.S. Pat. Nos. 3,876,089 (Moser), 4,055,265 (Eisenman), 4,664,583 (Gust), and 5,102,285 (Gust).
In order to prevent abrasive material from damaging the chains, some slat-type conveyors include flexible belting which spans the width between the chains. By way of example, U.S. Pat. No. 4,664,583 (Gust) discloses a slat-type conveyor in which a plurality of segmented belts are attached to the slats. U.S. Pat. No. 5,102,285 (Gust), in contrast, discloses a slat-type conveyor in which a single continuous belt which is wrapped around the chains and is affixed to the various slats. The single belt slat-type conveyor disclosed in U.S. Pat. No. 5,102,285 (Gust), however, suffers from noted deficiencies which will be discussed herein.
First, in order to prevent slipping, bunching, and/or stretching of the belt at the points where the chains reverse direction (i.e., at the ends of the generally obround chain loops), the pitch diameter of the chains must coincide with the pitch diameter of the belt. In order to align these pitch diameters, however, the chain loops must be located outboard (i.e., beyond the width) of the belt. As a result, the belt cannot be wrapped around the chain loops, but must instead be wrapped around the slats which interconnect the chain loops. Furthermore, single belt slat-type conveyors of this type are limited to only two chain loops (i.e., one chain loop on either side of the width of the belt).
Second, single belt slat-type conveyors of this type are expensive to manufacture and service. For instance, because the load of the cargo is ultimately shared by only two chain loops, both of these chains need to be very sturdy (i.e., large and expensive). In a like manner, the slats interconnecting the two chain loops need to be spaced-apart at relatively close intervals (i.e., numerous slats are required). Also, the belt needs to be joined to the slats at regular intervals. This not only significantly increases assembly labor, but also makes field disassembly and repair extremely difficult and time consuming.
Third, single belt slat-type conveyors of this type are subject to damage by the contents of the cargo. The slats, for example, are susceptible to deformation by rocks or other solid objects in the trailer. The chains are also prone to damage because they ultimately support the weight of the cargo. More significantly, however, should one of the chains break during use, virtually all of the slats would be destroyed.
Fourth, single belt slat-type conveyors of this type are subject to inherently high frictional losses caused, in part, by the weight of the cargo. More specifically, the weight of the cargo frequently causes the slats to wear or rub against the bed of the trailer which, in turn, increases the power requirements of the motor.